Generally, a hybrid vehicle has an internal-combustion engine, a first motor-generator, and a second motor-generator that are connected to a drive axle and wheels via a power splitting mechanism. The hybrid vehicle having such a configuration is designated as a split-type hybrid vehicle, or a series-parallel-type hybrid vehicle. A controller for the split-type hybrid vehicle is disclosed in a patent document 1 (i.e., Japanese Patent Laid-Open No. JP-A-2008-49829).
The controller includes a hybrid vehicle (HV) electronic control unit (ECU) that performs a total control of the hybrid vehicle, a motor-generator (MG) ECU for controlling each MG, and a first communication line that connects the HV ECU and the MG ECU in a one-to-one manner.
In addition, the controller for the hybrid vehicle may also be equipped with a second communication line, such as a CAN bus, and a brake ECU. The brake ECU controls a friction brake device and each of the MGs to provide a desired braking force as a sum total of a friction braking force and a regenerative braking force. That is, the brake ECU performs a cooperative control of the friction brake device and the MGs. The second communication line connects the HV ECU and other ECUs, including the brake ECU using two-way communications. That is, other than the brake ECU, an engine ECU is connected with the HV ECU via the second communication line. In the above, “CAN” is a registered trade mark.
The vehicle controller having the above configuration operates distributively and cooperatively. That is, in the conventional hybrid vehicle, the HV ECU calculates a total driving force of the entire vehicle, while calculating a demand torque of each of the MGs. Further, the communication between the HV ECU and the brake ECU via the second communication line enables the cooperative control of the braking force.
The above cooperative control scheme may be more efficiently implemented, if the demand torque of each of the MGs in a normal travel time is calculated in the MG ECU that obtains information about the rotation of each of the MGs. However, the demand torque calculated by the MG ECU may have to be transmitted to the brake ECU via the HV ECU. Therefore, in a transition state of the vehicle travel, which may be experienced when the vehicle travels on a bumpy road such as stone pavement or the like, the cooperative control of the braking force for the drive wheel may diverge, resulting in a series of grips and slips of the drive wheel. Such a divergence of the control may cause an excessive rotation of the first MG, for example, which may exceed a maximum number of rotations of, or example, 10,000 rpm or the like.